Enabling NOMA in Backscatter Reconfigurable Intelligent Surfaces-Aided Systems

One of the key enablers of future wireless communications is constituted by massive users can access the core network in wireless systems simultaneously, which can improve the spectral efficiency. In existing scheme of massive connections, namely non-orthogonal multiple access (NOMA), is investigated in conventional relaying networks. This method results in excessive power consumption and high hardware costs. Recently, reconfigurable intelligent surface (RIS) has been considered as one of the revolutionary technologies to enable energy-efficient and smart wireless communications, which is a two-dimensional structure with a large number of passive elements. This paper examines the RISs used in emerging communications systems based on NOMA scheme. The two-user system model contains the far user and the near user which employing RIS and NOMA is conducted in this study. In particular, we design two links (backscatter and direct links) to target to improve performance of far user. System performance was characterized through closed-form expressions of outage probability, ergodic capacity and throughput, which are beneficial to evaluate performance of two users. In Monte-Carlo simulations, it was revealed that the probability of the two users experiencing system outage was determined by factors related to power allocation, power transmission at the base station, and the number of reflecting elements in the RISs.